This application claims the priority benefit of Taiwan application serial no. 91118508, filed Aug. 16, 2002.
1. Field of Invention
The present invention relates to a cavity down ball grid array package structure. More particularly, the present invention relates to a cavity down ball grid array package capable of boosting electrical performance and lowering noise interference.
2. Description of Related Art
As techniques for manufacturing semiconductor devices continue to improve, high-tech electronic products are produced. Electronic products with personalized functions are appearing every day. Most electronic products are now designed to occupy as little space and weigh as little as possible. Yet, the products must be easy to use and feel comfortable. To fabricate a product with all the necessary functions and characteristic properties, the way the product is packaged is very important. Electronic devices are often packaged together inside a dual-in-line package (DIP), a ball grid array (BGA) or a tape automated bonding (TAB). In general, each packaging type has its special characteristics.
Among the conventional types of electronic packages, ball grid array (BGA) is most common. A back of a die is attached to the bonding pad on a substrate using an adhesive tape or other nonconductive adhesive materials. The bonding pads on the die and the contact points on the substrate are electrically connected using conductive wires. An encapsulation encloses the die, the conductive wires, and the contacts. In addition, a plurality of solder balls is planted onto the ball pads on the substrate so that the ball grid array may transmit electrical signals to the external circuit through the solder balls. Since the circuit layout on the BGA package is arranged in the form of an array, the package can accommodate a large number of external contacts.
However, as the size of each die shrinks, the level of integration increases correspondingly so that the amount of heat generated per unit area while the devices are working also increases proportionately. Hence, cooling is also an important consideration for the package designer. In general, a cavity down ball grid array (CDBGA) has a high heat dissipation capacity because the backside of the die is directly attached to a heat spreader. Through the heat spreader, heat generated with the package is directly conducted to the exterior.
FIG. 1 is a schematic cross-sectional view of a conventional cavity down ball grid array package. As shown in FIG. 1, the cavity down ball grid array package 100 includes a heat spreader 110, a substrate 120, a die 160, a plurality of conductive wires 170, an encapsulation 180 and a plurality of solder balls 190. The substrate 120 has a first surface 122 and a second surface 124. The first surface 122 of the substrate 120 is attached to the heat spreader 110 through non-conductive glue 192. The substrate 120 is a stack that includes four metallic layers 132, 134, 136, 138 isolated from each other by alternately positioned insulating layers 142, 144 and 146 respectively. The substrate 120 has a plurality of through holes 126, 128 that pass through the substrate 120. The interior of the through hole 126 contains a metallic layer 131 that links up the four metallic layers 132, 134, 136 and 138 electrically. The through hole 128 is wide enough to enclose the die 160. The substrate 120 further includes two solder mask layers 152, 154 formed on the first surface 122 and the second surface 124 of the substrate 120 respectively. The solder mask layer 154 has a plurality of openings 156 that exposes a portion of the uppermost metallic layer 132, thereby forming a number of contacts 130 and 133. The contacts 133 surround the through hole 128. In general, the bottom most metallic layer 138 in the substrate 120 also includes a ground plate 139 that serves as an earth connection.
The die 160 has an active surface 162 and a back surface 164. The active surface 162 of the die 160 has a plurality of bonding pads 166. The back surface 164 of the die 160 is attached to the heat spreader 110 through an adhesion layer 194. One end of each conductive wire 170 is bonded to a contact pad 166 while the other end of the conductive wire 170 is bonded to the contact 133 on the substrate 120. The encapsulation 180 fills up the leftover space within the through hole 128 so that the die 160, the conductive wires 170 and the contact pads 133 are all enclosed. The solder balls 190 are attached to the contacts 130 on the substrate 120. Through the solder balls 190, the substrate 120 connects electrically with an external circuit (not shown).
In the aforementioned cavity down ball grid array package 100, the ground plate 139 must have a horizontal area smaller than the substrate 120. If the ground plate 139 is small, noise interference will increase correspondingly. Hence, when the horizontal area of the substrate 120 is reduced due to miniaturization, horizontal area of the ground plate 139 is bound to decrease and noise interference is likely to have a significant effect. In addition, the radiation generated by a radio frequency circuit is likely to increase noise production. Under such circumstance, any decrease in area of the ground plate 139 may lower the noise fighting capacity resulting in the production of several interfering noise sources. Ultimately, logic circuit operations within the die 160 are likely affected.
Accordingly, one object of the present invention is to provide a cavity down ball grid array package having an anti-noise interference capacity.
A second object of this invention is to provide a cavity down ball grid array package having superior heat dissipation capacity.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a cavity down ball grid array package. The package includes at least a heat spreader, a substrate, a die, a plurality of conductive wires, an encapsulation and a plurality of solder balls. The substrate has a first surface and a second surface. The first surface of the substrate is attached to the heat spreader. The substrate has a through hole that passes through the substrate and exposes the heat spreader. The substrate and the heat spreader are electrically connected. The die has an active surface and a back surface. The die has a plurality of bonding pads on the active surface. The back surface of the die is attached to the heat spreader inside the through hole. One end of each conductive wire is electrically connected to a bonding pad and the other end of the conductive wire is electrically connected to the substrate. The encapsulation fills the through hole and encloses the die and the conductive wires. The solder balls are attached to the second surface of the substrate.
According to one embodiment of this invention, the first surface of the substrate is attached to the heat spreader through conductive glue. The substrate comprises of a stack of alternately positioned metallic circuit structures and dielectric structures. The dielectric structures have at least an opening that exposes the metallic circuit structures. The conductive glue is applied to the opening so that the conductive glue connects electrically with one of the metallic circuit structures. The heat spreader is made from copper. In addition, a nickel layer is also formed on the surface of the heat spreader. Furthermore, the heat spreader and a ground terminal are electrically connected through the substrate. In other words, the substrate can include a first ground terminal. The heat spreader and the first ground terminal are electrically connected through the conductive glue fills. In addition, the die may also include a second ground terminal and the heat spreader and the second ground terminal are electrically connected through the conductive glue fills.
Alternatively, in the foregoing package, the first surface of the substrate can be attached to the heat spreader through conductive glue with the substrate comprising alternately positioned metallic circuit structures and dielectric structures. The dielectric structures has at least an opening that exposes one of the metallic circuit structures, and the conductive glue fills the opening and connects with the metallic circuit structures electrically.
Also and, in the foregoing package, the first surface of the substrate can be attached to the heat spreader through conductive glue with the substrate comprising alternately positioned metallic circuit structures and dielectric structures. The dielectric structure attached to the heat spreader has at least an opening that exposes one of the metallic circuit structures, and the conductive glue fills the opening and connects with the metallic circuit structures electrically.
In brief, the heat spreader is electrically connected to the bonding pads on the substrate so that the heat spreader may serve as a ground. Since the heat spreader has a horizontal area much greater than the total area provided by the die and the substrate, noise interfering sources are greatly reduced. Moreover, the back of the die is directly attached to the heat spreader through an adhesive layer so that heat generated by the die is quickly removed by conduction through the heat spreader. Hence, the package has an efficient cooling system.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.